1. Field of the Invention
The present invention relates to physical quantity sensors that measure bearings and directions regarding physical quantities such as magnetism and gravitation. The present invention also relates to manufacturing methods of physical quantity sensors.
This application claims priorities on Japanese Patent Applications Nos. 2004-296371, 2005-45299, 2005-89629, and 2005-94388, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Recently, sensing technologies regarding measurement of bearings and directions in a three-dimensional space have been developed to provide various types of physical quantity sensors, such as magnetic sensors and acceleration sensors, which detect physical quantities such as magnetism and acceleration. For example, Japanese Unexamined Patent Application Publication No. 2004-128473 discloses an example of a magnetic sensor using a specially-designed lead frame.
It is known that physical quantity sensors are each equipped with physical quantity sensor chips (or magnetic sensor chips) which are mutually inclined with respect to each other. Due to the mutual inclination of paired physical quantity sensor chips, it is possible to detect magnetic factors lying in three directions (e.g., X-axis and Y-axis directions that are perpendicular to each other on the plane, as well as a Z-axis direction perpendicular to the X-axis and Y-axis directions); hence, it is possible to measure the direction of geomagnetism based on detected values as vectors existing in a three-dimensional space. Thus, it is possible to reduce the overall thickness of physical quantity sensors.
In addition to the aforementioned advantage in which physical quantity sensors each having mutually inclined physical quantity sensor chips can be reduced in the overall thickness thereof, it is possible to provide the following advantages.
For example, Japanese Unexamined Patent Application Publication No. H09-292408 teaches an example of an acceleration sensor, i.e., a physical quantity sensor of a one-sided beam structure in which a physical quantity sensor chip (i.e., an acceleration sensor chip) is inclined in advance with respect to a substrate therefor.
In the above, even when a sensor package is mounted on the surface of the substrate, it is possible to maintain a sensitivity in a prescribed axial direction in response to the inclination direction of the physical quantity sensor chip; and it is possible to reduce sensitivities in other axial directions including directions lying along the surface of the substrate. As a result, it is possible to maintain prescribed product characteristics in shipment.
Specifically, FIG. 17 shows a known structure of a physical quantity sensor 100 having an exterior mold portion 101 for fixing a pair of magnetic sensor chips 103, which are inclined with respect to each other, onto a bottom 102. The exterior mold portion 101 is molded using a resin. For this reason, side surfaces 105 of the exterior mold portion 101 generally have slopes that are each inclined in a thickness direction H by predetermined angles.
The aforementioned physical quantity sensor 100 can be adapted to a portable terminal device such as a portable telephone (or a cellular phone) having a navigation function, for example. Due to the recent tendency in which portable terminal devices have been reduced in dimensions, there may be a demand for the aforementioned physical quantity sensor 100 to be further reduced in dimensions. In order to realize compactness of the physical quantity sensor 100, it may be necessary to reduce dimensions G lying in a length direction W of the bottom 102 to as small as possible.
However, due to the slopes having prescribed angles adapted to the side surfaces 105 of the physical quantity sensor 100, both ends of the bottom 102 lying in the length direction W must be greatly projected outwardly beyond terminal ends 104 of the physical quantity sensor chips 103. This causes a bottleneck making it difficult further reduce dimensions of the physical quantity sensor 100.
Recently, portable terminal devices such as portable telephones (or cellular phones) have been equipped with GPS (Global Positioning System) functions for displaying users' present locations on earth. In addition, portable terminal devices can be further developed to have functions for precisely measuring geomagnetism and acceleration in addition to GPS functions; hence, it is possible for portable terminal devices held by users to measure bearings and directions thereof in a three-dimensional space as well as moving directions thereof.
In order to realize the aforementioned functions in portable terminal devices, it is necessary to incorporate physical quantity sensors such as magnetic sensors and acceleration sensors. In order to measure bearings and acceleration in a three-dimensional space, it is necessary that stages facilitating physical quantity sensor chips be inclined with respect to prescribed bases.
For example, one type of known magnetic sensor presently sold on the market is designed such that stages facilitating physical quantity sensor chips are not necessarily inclined with respect to prescribed bases. In this type of physical quantity sensor, there are provided a first magnetic sensor chip sensitive to magnetic factors lying in two directions (i.e., X-axis and Y-axis directions perpendicular to each other) of an external magnetic field and a second magnetic sensor chip sensitive to a magnetic factor lying in another direction (i.e., a Z-axis direction), wherein both the first and second magnetic sensor chips are mounted on the surface of a substrate.
The aforementioned magnetic sensor measures geomagnetic factors as vectors in a three-dimensional space based on magnetic factors detected by a pair of the first and second magnetic sensor chips.
However, the aforementioned magnetic sensor is basically designed such that the second magnetic sensor chip vertically stands on the surface of the substrate; hence, it is disadvantageous in that the thickness thereof (lying in the Z-axis direction) must be increased. In order to minimize the thickness, it is necessary to use physical quantity sensors in which stages facilitating physical quantity sensor chips are inclined with respect to prescribed bases. Examples have been disclosed in various papers such as Japanese Unexamined Patent Application Publications Nos. 2004-128473 and H09-292408, which have already been discussed above. In addition, Japanese Unexamined Patent Application Publication No. 2002-156204 discloses a magnetic sensor and an angle sensor having reduced dimensions.
As described above, a plurality of physical quantity sensor chips are mutually inclined with respect to each other inside of the physical quantity sensor, whereby it is possible to detect magnetic factors in three directions (i.e., X-axis, Y-axis, and Z-axis directions); hence, it is possible to measure the geomagnetic direction as vectors in a three-dimensional space on the basis of detection results. Due to the mutual inclination of physical quantity sensor chips, it is possible to reduce the height in the Z-axis direction; in other words, it is possible to minimize the thickness of the magnetic sensor.
In the above, it is required that an angle formed between two stages facilitating two magnetic sensor chips ranges from 0° to 90°. It is preferable that the angle be greater than 20°; and it is further preferable that the angle be greater than 30°. This is because a larger angle may improve the sensitivity lying in the Z-axis direction, which is well isolated from the X-axis and Y-axis directions.
As described above, physical quantity sensors in which physical quantity sensor chips are mutually inclined with respect to each other are advantageous in that the thickness thereof can be minimized so as to cope with downsizing of electronic devices, wherein they have various advantages due to the mutual inclination of physical quantity sensor chips and thus will contribute to mainstream technologies in the future.
An example of a physical quantity sensor in which physical quantity sensor chips are mutually inclined with respect to each other will be described with reference to FIG. 18. Physical quantity sensor chips are mounted on stages of a lead frame encapsulated in a resin mold package, wherein they are supported in a mutually inclined state by projections which project downwardly from stages towards the bottom of the resin mold package.
In manufacturing, a thin metal plate is subjected to press working so as to form the lead frame having the stages; then, projections are formed to project from the opposite ends of the lower surfaces (or back sides) of the stages. The lead frame is held and fixed in a pair of metal molds realizing a cavity of a prescribed shape therebetween, wherein the tip ends of the projections are pressed by the interior wall of the lower metal mold, so that the stages are rotated about axial lines relative to interconnection portions which are interconnected to the bases of the stages, and are thus appropriately bent; hence, the lead frame including the stages and projections is processed as shown in FIG. 18. Thereafter, a resin is introduced into the cavity of the metal molds. Thus, the opposite ends of the stages are respectively directed towards the upper surface of the resin mold package, whereby the stages are supported by the projections in a mutually inclined state.
In the aforementioned manufacturing method, the projections are subjected to pressing using a pair of metal molds, which are therefore likely to be damaged. In addition, it may require a troublesome work to precisely incline the stages by pressing.
As the stages of the lead frame are subjected to inclination using the upper and lower molds by way of the projections, which project from the stages, the physical quantity sensor has a drawback in that the overall size of the package encapsulating the lead frame and physical quantity sensor chips is increased due to the provision of the projections.